RE: MODERN BIRDS AND MIGRATION

["Stewart, Dwight" <Dwight.Stewart@VLSI.com>]

   I read somewhere fairly recently (in the National Geographic, I think)
that at least some migratory birds have small granules of magnetic metal in
their heads.  The theory went that perhaps they are able to follow the
Earth's magnetic field due to this.  I'm not sure about migrating birds
simply going along with the trade winds, although it does make sense.  I
don't believe the whooping crane that migrates to Texas once per year is
following a trade wind, however.  But, maybe some birds do & some don't.

Dwight

        -----Original Message-----
        From:   Betty Cunningham [SMTP:bettyc@flyinggoat.com]
        Sent:   Wednesday, September 09, 1998 7:31 PM
        To:     Matthew Troutman
        Cc:     dinosaur@usc.edu; dgrayshan@tschan-partner.com
        Subject:        Re: MODERN BIRDS AND MIGRATION

        It's also likely that tradewinds will affect migratory behavior-if
it's
        easier to fly long distances via a high altitude tradewind, you
might
        not find migratory animals travelling out of this 'byway'.  
        You might try checking this theory if idyllic spots that are not
along a
        byway are bypassed for those that are, even when further away.
        However in the case of fossil birds I have no idea how you would try
and
        identify mesozoic tradewinds.

        -Betty Cunningham

        Matthew Troutman wrote:
        ('cause David asked)
        > <<Thirdly, is it known or is there a good theory as to why birds
migrate
        > in the way they do? The Godwits migrate vast, distances, for
example,
        > from Northern Europe to New Zealand. Why so far? If it's just food
or
        > water there's plenty of that a lot nearer than New Zealand.
Migratory
        > behaviour is predictable, regular, systematic, in fact, highly
evolved.
        > Are there many species that travel similar distances to the
Godwits, or
        > are they unique?>>
        > 
        > Long migration distances in birds is certainly not unique amoug
        > vertebrates (or even animals).  So far, the best theory (in my
opinion)
        > is that long migrations are charged by the changing seasons in
temperate
        > zones and at the poles.  Moving away from birds for a second, look
at
        > the variation in spring and summer habitats for North
American/South
        > American vespertillonid bats.  Some individuals stay near Panama,
        > whereas others summer as far north as near the Artic Circle!  It
all has
        > to do, probably with how their ancestors migrated, because a bird
or bat
        > seems to not be able to migrate without doing so with its parents
and/or
        > "flock".  As for long distances travelled by terns and godwits, it
was
        > probably a gradual trend for some individuals to travel far North
and
        > South.  Another factor might be certain individuals or flocks
watching
        > other individuals for flocks.